HBV Vectors and Cells for Producing the Same This invention relates to HBV vectors, processes for the provision thereof and cells usable for this purpose as well as the use of the HBV vectors.
Efficient methods are required for a gene therapy to transfer a xe2x80x9ctherapeuticxe2x80x9d DNA into select target organs. Up to the present, retroviral vectors have been used above all for this purpose. However, they have the drawback that the cells to be treated first have to be propagated in vitro, infected and then be transferred into the patient again. However, it should be the objective of a gene therapy to treat cells in situ.
For an in vivo gene therapy the strict organ specificity of the employed vector system is an absolute precondition. The hepatocytes of the liver are of special interest for this purpose. The liver is the source of most of the serum proteins and plays a central part for the regulation of the metabolism in the peripheral organs. Therefore, a plurality of different, inherited metabolic defects manifest themselves in the liver. In addition, the liver is also affected in the case of some viral infections which can be treated only very poorly. Furthermore, the liver could be used as a bioreactor for the secretion of diverse proteins, provided that a suitable gene transfer system existed. Thus, new paths could be trodden also for the treatment of diseases which do not manifest themselves in the liver.
However, a liver cell-specific gene transfer system for which an in vivo application could be in consideration does not yet exist.
Therefore, it is the object of the present invention to provide a gene transfer system which is liver cell-specific and suitable for an in vivo gene therapy.
According to the invention this is achieved by the subject matters in the claims.
Therefore, the subject matter of the present invention relates to a HBV vector in which functional genes of HBV are at least partially deleted.
The expression xe2x80x9cHBVxe2x80x9d refers to hepatitis B virus. This is a DNA virus having a genome length of 3.2 kb. The genome of hepatitis B virus contains four partially overlapping open reading frames (ORF): the pol-ORF (HBV polymerase), the S-ORFs (surface proteins), the C-ORFs (capsid proteins) and the X-ORF (viral transactivator) Hepatitis B virus is liver cell-specific.
The expression xe2x80x9cHBV vectorxe2x80x9d comprises any HBV vector which is suitable for a gene transfer, especially in a gene therapy, most especially in an in vivo gene therapy. In this connection, the expression xe2x80x9cvectorxe2x80x9d relates to a DNA molecule as well as a virus particle.
The expression xe2x80x9cin which functional genes of HBV are at least partially deletedxe2x80x9d refers to the fact that in an HBV vector according to the invention one to all genes necessary for the replication of HBV are partially or fully deleted. Such genes are especially those which code for polymerase, the surface proteins and the capsid proteins of HBV. Because of the above deletion, an HBV vector according to the invention can no longer replicate independently in a eukaryotic cell.
It is advantageous when in an HBV vector according to the invention the genes for the polymerase, the surface proteins and the capsid proteins of HBV are at least partially deleted. It is especially advantageous when these genes are fully deleted.
Furthermore, it is of advantage when in an HBV vector according to the invention the gene of the transactivator of HBV is also mutated or partially deleted and fully deleted, respectively.
A preferred HBV vector of the present invention is pHBV/V1. Its DNA sequence is indicated in FIG. 1. In pHBV/V1, the genes for the polymerase, the surface proteins and the capsid proteins of HBV are fully deleted. Likewise, the gene for the transactivator of HBV has an ochre mutation. pHBV/V1 was deposited with the DSM (Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH [German-type collection of micro-organisms and cell cultures]Mascheroder Weg 1b, D-38124 Braunschweig, Germany) under DSM 9947 on May 3, 1995.
Because of its deletion, an exogeneous or foreign or heterologous DNA can be inserted in an HBV vector according to the invention, and it can then be expressed in the cells accommodating the HBV vector. A foreign DNA may be any DNA, particularly a diagnostically and/or therapeutically effective gene. The length of the foreign DNA may vary, it being advantageous when it does not exceed about 3 kb. On a protein basis, this length corresponds to a molecular weight of over 100,000, which is quite sufficient for gene-therapeutic applications.
A foreign DNA is inserted in an HBV vector according to the invention via the xe2x80x9cmultiple cloning sitexe2x80x9d of the latter. Hence it is also possible to insert the foreign DNA between two inverse terminal repetitions of adeno-associated viruses. This would increase the integration frequency as well as the integration specificity of the foreign DNA in a special chromosome.
Another subject matter of the present invention relates to a process for producing the above HBV vectors. In such a process, the defect in the independent replication of an HBV vector according to the invention is overcome by transfecting it into cells which express functional HBV proteins. The expression of the HBV proteins can be transient and/or stable, a stable expression being preferred. HBV vectors are provided as DNA molecules as well as virus particles by the process according to the invention.
Common methods can be used for producing the above cells. It is favorable to transfect hepatoma cells, e.g. Hep G2 cells (cf. Knowles, B. B. et al., Science 209 (1980), 497-499) with expression plasmids coding for functional HBV proteins. It is especially favorable when the genes for the individual functional HBV proteins are present on differing expression plasmids.
For the preparation of the above expression plasmids, it proves to be favorable to use common HBV vectors having selection markers and delete therein the epsilon region necessary for packaging as well as differing functional HBV genes. The DNA sequence of HBV, including the epsilon region, is known (cf. e.g. Fujiyama, A. et al., Nucl. Acids Res. 13, (1983), 4601-4610; Polack, J. R. and Ganem, D., J. Virol. 67, (1993), 3254-3263).
Common methods can be used for the transfection of hepatoma cells, e.g. Hep G2 cells, having the above expression plasmids. For example, a DEAE-dextran process (cf. McCutchan, J. H. and Pagano, J. S., J. Natl. Cancer Inst. 41, (1968), 351-357) is suitable for a transient expression of the functional HBV proteins, whereas e.g. a calcium phosphate precipitation process (cf. Graham, F. L. and van der Eb, A. J., Virology, 52 (1973), 456-467) has to be mentioned for a stable expression. Cells are obtained which express functional HBV proteins. Such cells also represent a subject matter of the present invention. Of these those are preferred which express the polymerase, the surface antigens and the capsid proteins of HBV, particularly express them in stable fashion.
The present invention serves for providing a gene transfer system which is liver cell-specific and suitable for a gene therapy, particularly an in vivo gene therapy. The gene transfer system comprises HBV vectors and cells in which these vectors can be provided.
The present invention enables to transfer foreign DNA into liver cells where it is expressed. Thus, it does not only open up possibilities of treating monogenic metabolic defects, e.g. familial hypercholesterolemia, hyper-ammonemia, hyperbilirubinemia, phenylketonuria, xcex11-antitrypsin deficiency, hemophilia, etc., but also of treating multifactorial diseases such as the virus hepatitises, e.g. HBV, HCV, HDV, and last but not least the primary liver cell carcinoma.
In addition, the present invention provides the possibility of using the liver as bioreactor for the secretion of any therapeutic proteins into the blood. This results in new aspects of gene therapy, which exceed by far the original target organ, such as the treatment of malignant diseases, of viral infections or generally of diseases which do not manifest themselves in the liver.
Moreover, by means of the present invention it ispossible to monitor the most differing processes for killing viruses in body fluids withdrawn, e.g. blood. For this purpose, an HBV vector according to the invention, which is provided with a minotor gene, can be added to the body fluid before the process starts and then be determined at certain intervals.
Thus, the present invention is perfectly suited as a reagent for diagnosis and/or treatment.